Manufacture of refined wax



Nov. 15, 1955 S. F. PERRY ETA!- MANUFACTURE OF REFINED WAX Filed April8, 1953 DEWAXING 3 SOLVENT l T 4 '4\,SOLVENT l 7 SLACK WAX 5 SOLVENT 2 iCHILLER FILTER :2 WAXY DIST. 8

H l 4 s: h 13 I6 I5 WAX s2 29 35 22; SWEATER QWEATER 51 1,36 Luke LOWBOILING OIL STEPHEN F. PERRY HERMAN J. ZOELLER RANDOLPH M. BAILLYINVENTORS I BYw, ATTORNEY United States Patent and Randolph M. Bailly,Little Silver, 'N..J., assignors to Esso Research andEngineeringCompany, a corporation of Delaware .ApplicationAprilS,1953,Serial No. 347,576

3 Claims. (Cl. "19617) The present invention is concerned with theproduction of a high quality paratfin wax. The inventionis morespecifically directed toward the more efiicient removal of small tracesof oil by an improved sweating operation. In accordance with the presentinvention, a small quantity of a relatively low boiling oil .is added tothe wax prior to sweating the same under conditions to securesubstantially complete and efficient removal of the undesirable oilconstituents.

In the refining of hydrocarbon oils such .as petroleum oils, it is knownto segregate para'fiin waxes from socalled parafiin distillates, waxylubesand the like. "The segregation of these waxes is secured by anumber of processes. For example, it is known to chill the selectedwax-containing fraction in order to secure crystallization of the waxand to remove the wax crystals from the oil by filtering, centrifugingand the like. It is 'also known to use various dewaxing solvents such asliquid'normally gaseous hydrocarbons, such as propane,-butane, as wellas other solvents, such as methyl-ethyl ketone and the like. It is alsoknown to utilize in dewaxing operations solvent mixtures wherein onesolvent-comprises a wax precipitating solvent while the other comprisesa solvent having a high solubility for oil. A .solvent mixture of thischaracter, for example, comprises about 60% by volume of methyl-ethylketone and about 40% by vdlume of toluene. In utilizing a solventmixture of this character, it has been the practice to add the mixturein toto or incrementally to the waxy distillate asit 'is being chiled.In dewaxing operationsfitis also knownto use various filter aids andother agentsin order to render the dewaxing and filtering operationsmore efiicient.

The wax segregated from the hydrocarbon oil, .usually termed, slack wax,contains from about to 40% of oil. The slack wax isre'fined usually byconventional sweating to produce crude scale wax ina manner to reducethe oil content to less than about 5% by weight. The slack wax may .bedistilled to-obtain the desired boiling range prior to sweating, ifdesired. This crude scale wax generally has an oil content of about 2%to 3% by weight.

At the present time two major methods are employed for producing refinedparaffin wax (02% or less oil content) from scale wax (2 to 3% oilcontent). The older of these, the sweating process, has been used formany years without important modifications. This .process is suitableonly for refining the waxes present in relatively low viscosity stocks.The newer deoiling .process utilizes a suitable selective solvent whichdissolves the oil and does not dissolve the wax. This method may beemployed in crystallizing wax from both.low and high viscosity stocks.

The older sweating method of .deoiling consists of chilling the warm,liquid scale wax in pans until it is solid, then slowly raising thetemperature, during which time the entrained oil drains awayfirst,.followed by;lower melting point waxes as the temperature :rises,leaving-the desired product. In general, sweating "iswa ratherineflicient methodin the utilization "of heat, itime 1reqtiired tocomplete the cycle, and degree of fractionation robr CC 2 tained percycle. Although sweating separates'waxes by melting point, the majorfactor .to be considered when sweating scale to refined wax is the oilcontent of the refined sweater product. If the oil present is over theamount allowed, the'sweating is continued even though much Wax of thedesired melting point runs into intermediate cuts which must berecycled.

It has now been found that the addition of a small percentage of a lowerboiling hydrocarbon to scale Wax will greatly accelerate the removal ofoil. in the sweating operation and give a product of lower oil contentwithout any loss in yield of wax or sweater capacity. 'Melting pointseparation is also improved. 'In commercial practice it is contemplatedthat a heavy naphtha or kerosene fraction be employed. This technique isapplicable only where a subsequent stripping or distillation step isused, which will .remove any traces of the added light oil from thefinal wax .product and thus prevent .an odor problem.

The lower wax oil content readily obtained by the practice of thisinvention results in improved color, stability and tensile strength, andeases the load on any treating step and on the bauxite :filtration stepemployed for final purification .of the wax. Furthermore, an additional10-15% increase in yield and plant capacity is realized with the presenttechnique as compared to conventional sweating when sweating to the sameoil content of about 0.2%.

In the manufacture of refined .parafiin wax from the wax bearingpetroleum distillates,conventional processing sequence calls for aninitial dewaxing step to remove the 'bulk of the oil from thewax-bearing stream, deoiling the resultant wax to a suitable oilcontent, chemical treating the low oil content wax in order to stabilizethe oil, and finally bauxite or clayfiltering to improve color,

odor and taste. One of the quality .tests that the finished paraffin waxproduct is required to meet is the U. S. Pharmacopeia .(U. .S. P.)AcidTest. This test, desig nated as A. S. T. M. D612-45, is a measure ofpurity and determines the relative amounts of carbonizable materialin'the wax. By spectroscopic studies it has been determined that the oilremaining in the wax contains the constituents responsible for theparafiin wax passing or not passing the U. S. Pharmacopeia (U. S. P.)Purity Test. Therefore, any treatment given the oil, per set, will 'bereflected in the quality of the finished refined wax. Furtherspectroscopic studies have indicated that the 2 and 3 ring aromaticconstituents inthe oil contained .in .the wax are responsible for the'failure of the wax to pass U. S. P. Acid Test=7650 times K when K330 isthe optical density in units 'ofJliters/gm-cm.

Acid treating the wax, as expected, does improve the U. S. P. AcidTeston refined wax due to the acid. reacting 1 Parafiin is listed in theU. S. Pharmacopeia with specifications which include that it must passthe U. S. P. Acid .Test. This test is applicable to parafiin wax toascertain whether it conforms to the standard of quality required forpharmw ceutical, food and drug uses.

The test procedure is as fo1lows: 5 m1. of wax and 5 ml. of 94.7% (i0.2)sulfuric acid are contacted at 157 F. for six minutes with intermittentmixing and settling intervals. The

resultant color of the acid layer is compared with a standard colorsystem. An arbitrarily chosen color standard of 5 or less is consideredsatisfactory. A color darker than 5 is considered not passing If notpassing the paratfin wax contains carbonizablc material making it unfitfor use in connection with cosmetics, foods and drugs. .This is the sametest formerly listed in the National Formularyand. called the N. F, AcidTest.

carbon fractions.

with the 2 and 3 ring aromatics. The reaction products are removed byneutralization and'water washing. Deoiling and melting point separationby sweating will also reduce the 2 and 3 ring aromatics in the parafiinwax as the oil content is reduced. However, sweating alone will notreduce the aromatic content sufiiciently low enough for the wax to passthe U. S. P. Acid Purity Test without a further chemical treatmentunless the sweating is carried to an uneconomical extreme. The finalpercolation step through bauxite or clay also reduces the U. S. P. AcidTest indication but only approximately 50% under normal conditions. Thisalone is not sufiicient for obtaining a paraffin wax of the desiredpurity as measured by passing the U. S. P. Similarly, the constituentsre sponsible for the poor heat stabilityof certain waxes have beenisolated in the aromatic portion of the oil content of the wax.

In accordance with the present invention, instead of acid treating thewax, which requires large quantities of chemicals, extraneous equipment,and also presents sludge disposal problems, the scale wax prior tosweating is blended with a small quantity of a low boiling oil such as aheavy naphtha fraction (boiling range 230-430 F.), a kerosene fraction(boiling range about 350500 F.) or with constituents such as toluene andheptane. In general, the final boiling pointof the low boiling oil addedshould be at least 100 F. and preferably 150 F. lower than the initialboiling point of the wax fraction being deoiled.

In general, wax fractions boil at atmosphericpressure in the range fromabout 600 F. to 950 F. However, these waxes are normally distilled atabout mm. pressure wherein the initial boiling point is about 370 F.,90% at about 550 F. and final boiling point at about 600 F. Thus, it isdesirable that the final boiling point of the added oil not exceed about500 F.

By this procedure the concentration of undesirable,

. reactive constituents in the oil contained in the wax is materiallyreduced. Furthermore, the viscosity of the oil is lowered, whichimproves the efiiciency of sweating. In the subsequent sweatingoperations the bulk of the added low boiling oil together with thenative oil is removed in the initial sweater cuts and the sweater yieldsfor a given native oil content is materially improved.

The process of the present invention may be fully understood byreference to the drawing illustrating one embodiment of the same.Referring specifically to ,the

' drawing, a waxy crude oil is introduced into distillation zone 1 bymeans of feed line 2. Temperature and pressure conditions in zone 1 areadapted to remove overhead by means of lines3 and 4 the'low boilinghydro- A waxy distillate fraction is removed as a side stream by meansof line 5, while a residual oil is removed by means of line 6.

The waxy distillate flows through a chilling zone 7 .which may comprisea plurality of chilling stages wherein the temperature of the waxydistillate is progressively reduced. A typical operation is tointroduce'the feedv oil into an initial chilling stage at a temperatureof about 130 F.; to introduce the feed oil into the second chillingstage at atemperature of about 90 F.; to introduce the feed oil to thethird chilling stage at atemperature of about 60 F.; to introduce thefeed oil to the fourth chilling stage at a temperature of about 25 F.and .to chill the same in the fourth chilling stage to a temperature inthe range from about 10 to +10 F. The operation of the respectivechilling stages may be varied appreciably and either direct or indirectchilling means utilized. For purposes of illustration, it is assumedthat a solvent mixture is used and that the wax-precipitant comprisesmethyl-ethyl ketone and that the aromatic solvent having a highsolubility for oil comprises toluene. It is also assumed that 3 to 4volumes of total solvent mixture is utilized per volume of waxy oilbeing dewaxed. The solvent mixture comprises 75% by volume ofmethylethyl ltetone and 25% by volume of toluene.

The entire mixture comprising oily constituents, crystallized waxconstituents, toluene and methyl-ethyl ketone, after chilling is held atthe filtering temperature and passed to filtering zone 8 wherein thesolid wax particles are segregated from the oily constituents by anysuitable filtering or separation means. The filtering zone may comprisedrum filters, plate and frame presses, centrifuges or suitableequivalent equipment for the separation of the precipitated waxyconstituents from the oily constituents.

The oil and a portion of the solvent are removed from zone 8 by means ofline 9 and the wax cake washed with a wash solvent introduced intofiltering zone 8 by means of line 10. Slack wax and solvent are removedfrom zone 8 by means of line 11 and passed to a distillation zone 12wherein a separation is made between the wax and the solvent. It is tobe understood that other means of separating the solvent from the waxmay be utilized if desirable. a v

The wax substantially free of solvent is removed from separation zone 12by means of line 13. The-solvent mixture comprising methyl-ethyl ketoneand toluene is removed overhead from zone 12 by means of line 14 andpreferably recycled to the system. The oil-solvent mixture removed fromfiltering zone 8 by means of line 9 is introduced into a distillationzone wherein a separation is made between the oily constituents and thesolvent mixture. 7

While the drawing illustrates a solvent dewaxing operation with respectto the production of the slack wax,

it is to be understood that the waxy constituents may also be separatedin a conventional plate-and-frame pressing .operation. The slack wax maybe further refined to crude scale wax in zone 15, which comprises aconventional sweating operation, or solvent deoiling operation, or thelike. The oil removed from zone 15 by .means of line 36 may preferablybe recycled to zone 7.

However, in accordance with the present invention, a

low boiling oil is added to the scale wax by means of line 50. Themixture is passed to sweating zone 16 wherein the same is solidified bycooling and then. exposed'to progressively higher temperatures. By thisprocedure the quantity of 2 and 3 ring aromatics in the wax product ismaterially reduced. The bulk of these compounds is removed from thesweated wax by means of line 51. Wax fractions of desirable quality; areremoved from zone 16 by means of line 29.

The fraction removed by means of line 29 is then passed into adistillation zone 60 wherein temperature and pressure conditions areadjusted to remove overhead by means of line 61 the low boiling oil andto remove by means of lines 62 and 63 high quality wax fractions.

The invention is broadly concerned with the more complete removal ofoily constituents from scale wax in order to improve the quality of thewax. This is secured by adding to the wax from 1 to 5, preferably from 2to 3 volumes of a lower boiling oil per volme of oil remaining in thescale wax, and then subjecting the same to a sweating operation. Sincethe oily constituents or the scale wax amount to from 1% to 5% by volumethereof, the amount of lower boiling oil added is therefore broadly from1% to 25 by volume based on the scale wax.

As pointed out heretofore, preferred oils to be added compriseindividual hydrocarbons such as toluene and heptane. process to employheavy naphtha fractions and kerosene fractions. In general a spread ofat least F. should exist between the final boiling point of the oiladded and the initial boiling point of the wax fraction to be deoiled.

The process of the present invention may be more same.

However, it is within the concept of the present Table SVVEATING OFCRUDE SCALE TO REFINED VAX \VITH AND WITHOUT LOWER BOILING HYDROCARBONDILUTION 4 Parts Toluene to 1 Part Original Oil Oil Dilution NoneSweater Charge:

Melting Point, F Percent Oil, ASTM U. V. Absorption (Km) Refined Wax(sweated, stripped to remolve diluent and Bauxite filtered 25 YieldBased on Sweater Charge, Wt.

Percent .i 33.5 33.8 34.9 Yield Based on Wax Charge, Wt.

Percent 33.5 38.6 39.8

1 Calculated from Km. A value of 5 or less is satisfactory. Chemicaltreatment (omitted in this workup) will improve the U. S. P. Acid Test.A milder treatment would Suffice when using a diluent in sweating and inmany cases could be omitted altogether.

What is claimed is:

1. Process for the production of a high quality parafiin wax of improvedstability, which comprises segregating a molten scale wax comprisingabout 15% by volume of oil, adding to said molten scale wax ahydrocarbon oil having a final boiling point at least less than theinitial boiling point of said scale wax in an amount of from about 1% toabout 25% by volume of said scale wax, thereafter solidifying theresultant mixture of said molten wax and said hydrocarbon oil andsubsequently sweating the solidified mixture to produce a wax of reducedoil content, and thereafter distilling said wax of reduced oil contentto completely remove said lower boiling hydrocarbon oil.

2. Process according to claim 1 wherein said mixture of said wax andsaid hydrocarbon oil is sweated to an oil content of less than 0.2% byvolume of oil.

3. Process according to claim 1 wherein said mixture of said hydrocarbonoil and said wax is sweated to an oil content of less than about 0.1% byvolume of oil.

References Cited in the file of this patent UNITED STATES PATENTS1,910,920 Higgins May 23, 1933 2,099,683 Ferris et a1. Nov. 23, 19372,658,852 Tiedje et al Nov. 10, 1953

1. PROCESS FOR THE PRODUCTION OF A HIGH QUALITY PARAFFIN WAX OF IMPROVEDSTABILITY, WHICH COMPRISES SEGREGATING A MOLTEN SCALE WAX COMPRISINGABOUT 1-5% BY VOLUME OF OIL, ADDING TO SAID MOLTEN SCALE WAX AHYDROCARBON OIL HAVING A FINAL BOILING POINT AT LEAST 100* LESS THAN THEINITIAL BOILING POINT OF SAID SCALE WAX IN AN AMOUNT OF FROM ABOUT 1% TOABOUT 25% BY VOLUME OF SAID SCALE WAX, THEREAFTER SOLIDIFYING THERESULTANT MIXTURE OF SAID MOLTEN WAX AND SAID HYDROCARBON OIL ANDSUBSEQUENTLY SWEATING THE SOLIDIFIED MIXTURE TO PRODUCT A WAX OF REDUCEDOIL CONTENT, AND THEREAFTER DISTILLING SAID WAX OF REDUCED OIL CONTENTTO COMPLETELY REMOVE SAID LOWER BOILING HYDROCARBON OIL.